Sarah Crompton was carried along by the cleverness of Nightmare in Silver, the
latest episode in the new series of Doctor Who, BBC One.

This season’s series of Doctor Who has been what can only be described as patchy. It has also fiercely divided opinion. My 12-year-old son adored Journey to the Centre of the Tardis, an episode that grown-up critics slated; he hated The Crimson Horror, written by smarty-pants Mark Gatiss and much admired by me, not least for a lip-smacking performance byDame Diana Rigg and a poignant one by her daughter, Rachael Stirling.

This penultimate effort Nightmare in Silver, had exactly the same Marmite effect. It was written by Neil Gaiman, who took the Doctor, Clara and her two young - and rather tiresome - charges to the biggest amusement park in the universe, now lying derelict and sadly neglected. There they met the charismatic dwarf Porridge, played with beautiful lightness of touch by Warwick Davis and the vaguely sinister Mr Webley (Jason Watkins).

The star attraction in Webley’s World of Wonders was a Cyberman, apparently sleeping, but manipulated by Porridge into playing chess. But then shiny little cybermites slithered out of the sleek machine's neck, and it was quite clear that trouble was afoot. Before we knew it, an entire army of Cybermen was ready to invade and the Doctor was battling a cyber intruder inside his own brain.

It was all very clever and whipped along at a quickfire pace - so rapid in fact that if you blinked you would have missed poor old Tamzin Outhwaite's guest appearance. But I loved the way that this episode actually looked like proper sci-fi, with ghostly grey vistas of the abandoned theme park looming under dark skies; I also admired the script which was full of humour and sharp lines including a wonderful, musing payoff from the Doctor to Clara: “Oh you mystery wrapped in an enigma squeezed in a skirt that’s just a little bit too tight.”

Yet the witty intelligence of that quotation - one for the grown-ups - did indicate the problem with the episode as a whole. A large chunk of it took place inside the Doctor’s head, as the Time Lord struggled to defeat his cyber double in a game of chess with the entire universe at stake. This gave Matt Smith a brilliant opportunity for some dexterous and compelling acting, switching effortlessly between the two personae.

But the acting masterclass went on a bit long for the 12 year-olds; even for their mother, it could have done with a bit more variation in pace and tone. On the other hand, Gaiman said his aim was to make the Cybermen scary again, and in this he utterly suceeded. With their blank black eyes and their ability to upgrade instantly, they are the ultimate baddie: implacable, inhuman and conquerable only by a superhuman force.

The sight of their awakening in massed ranks, an alien silver army, will stay with me for some time.